1. Field of the Invention
The present invention relates to an ejector controller of an injection molding machine, and more particularly relates to an ejector controller in which breakdown of a core of a die or the like is prevented by the ejector operation.
2. Description of the Prior Art
It has been performed to detect a load applied to an ejector pin, in order to prevent the ejector pin, a core of a die, or the like from being broken down because of making an error in setting the projecting amount of the ejector pin so that an abnormal load may be applied to the ejector pin, and further, in order to prevent an ejector pin, a core body, a core, or the like from being broken down because of causing an interference between the ejector pin and the core body or the like so that an abnormal load may be applied to the ejector pin or the core body, and furthermore, in order to detect the fact that a molded part is left in the die or the like.
Especially, in an electrically powered ejector mechanism in which an ejector mechanism is driven by a servomotor, the following procedures are disclosed in Japanese Patent Application Laid-Open No. 10-119107:
A disturbance estimating observer is assembled in a servo circuit of a servomotor for driving and controlling an ejector axis, and a disturbance load torque is estimated by the above described disturbance estimating observer, and this estimated disturbance load torque is compared with a set permissible value for each specific period, and a timer is started at the time when the estimated disturbance load torque exceeds the permissible set value, and in the case where disturbance load torque exceeding the set permissible value is continuously detected over the set permissible time, it is detected that a collision occurs between an ejector rod and another object, and an abnormal signal is issued to stop the ejector axis driving servomotor.
In the above described procedures in which the estimated disturbance load torque determined by the disturbance estimating observer is compared with the set permissible value to detect an abnormal load, it is necessary to set a permissible value. Since the permissible range of the load is different and also the frictional torque applied to the ejector rod is different depending on dies, the set permissible value for judging that a load is abnormal is also different depending on the die. Therefore, it is necessary to set a permissible value for judging this load abnormality each time the die is exchanged. When the maximum value within the optimum permissible range is not set as the permissible value and a set value larger than the maximum value of this permissible range is set, there is a possibility of breaking down the core of the die.
Furthermore, when a permissible value smaller than the maximum value within the per missible range is set, the disturbance load torque which changes according to the variation of the frictional force of an ejector plate or an ejector pin or the like in each ejector operation exceeds this set permissible value, and an alarm or the like is outputted for a load abnormality to stop the operation, in spite of a normal ejector operation, and consequently, the production efficiency is lowered.
Therefore, it is necessary to set the permissible value for judging an abnormal load at an optimum value for each die. However, as mentioned above, this permissible value changes depending on dies, and therefore, it is necessary for an operator who sets the permissible value to have knowledge and experience of dies. Furthermore, even when the operator has knowledge and experience thereof, it is very difficult to set the optimum permissible value.
It is an object of the present invention to provide an ejector controller of an injection molding machine in which it is unnecessary for the operator to set a value for judging an abnormal load from the estimated disturbance load torque and the value can automatically be set.
In the ejector controller of an injection molding machine according to the present invention, load detecting means for detecting a load applied to a servomotor which drives the ejector axis is assembled in the controller, and the load applied to the servomotor at the time of the ejector operation for each molding cycle is detected by means of the load detecting means. Then, the loads for the latest one or a plurality of ejector operations before the present molding cycle are stored in storing means with respect to the time or the ejector positions. Means for obtaining a reference load from the stored load, and means for determining a permissible upper limit value from the reference load are provided, and further, discriminating means for outputting an abnormal signal when the load at the time of the present ejector operation exceeds the above described permissible upper limit value is provided.
The ejector controller of an injection molding machine according to the present invention can employ the following embodiments:
When an abnormal signal is outputted, the load applied to the servomotor at the time of that ejector operation is excluded from the data for determining the reference load.
Any permissible upper limit value is set on the screen. Furthermore, the load applied to the servomotor at the time of the present ejector operation, the reference load and the permissible upper limit value, or a deviation between the reference load and the load at the time of the present ejector operation are graphically displayed on the screen with respect to the time or the ejector position.
A permissible lower limit value is also determined by the above described means for determining the permissible upper limit value from the reference load, and the above described discriminating means also outputs an abnormal signal when the load applied to the servomotor at the time of the present ejector operation exceeds the above described permissible lower limit value.
For a predetermined number of cycles after starting of a full automatic molding, the load applied to the servomotor is excluded from the data for determining the reference load. Furthermore, this predetermined number of cycles after starting of a full automatic molding for which the load applied to the servomotor is excluded from the data for determining the reference load is set on the screen of display means. The above reference load is determined by the average value of the loads applied to the servomotor at the time of the ejector operation in a plurality of molding cycles before the present molding cycle.
The above described detecting means for detecting a load applied to the servomotor is a disturbance estimating observer. The disturbance estimating observer estimates a load as a load torque.
According to the present invention, as for the permissible range for the discrimination of an abnormal load in the ejector operation, the reference disturbance load torque is automatically determined from the estimated disturbance load torques obtained at the time of a plurality of times of normal ejector operations just before the present molding cycle, and on the basis of this reference disturbance load torque, the discrimination of an abnormal load is performed, and therefore, it is unnecessary for the operator to set the reference value for the discrimination of an abnormal load. Furthermore, the reference disturbance load torque is determined on the basis of the data obtained in the normal ejector operation, and an abnormal load is discriminated by using the permissible range determined by this reference disturbance load torque, and therefore, the discrimination of an abnormal load is more accurately and optimally performed. Furthermore, the permissible range determined by the reference disturbance load torque is not a uniform value, but a waveform during an eject stroke, and therefore, it becomes an optimum permissible range corresponding to the position of the ejector pin, so that an abnormal load can be discriminated more accurately.